This invention relates to optical fiber canisters, and, more particularly, to the construction of such a canister designed to damp the rotational motion of the optical fiber as it is payed out.
Optical fibers are strands of glass fiber processed so that light transmitted therethrough is subject to total internal reflection. A large fraction of the incident intensity of light directed into the optical fiber is received at the other end of the optical fiber, even through the optical fiber may be hundreds or thousands of meters long. Optical fibers have shown great promise in communications applications, because a high density of information may be carried bidirectionally along the optical fiber and because the quality of the signal is less subject to external interferences of various types than are electrical signals carried on metallic wires. Moreover, the glass fibers are light in weight and made from a highly plentiful substance, silicon dioxide.
Glass optical fibers are typically fabricated by preparing a preform of glasses of two different optical indices of refraction, one inside the other, and processing the preform to a fiber. The optical fiber is coated with a polymer layer of a material such as a urethane acrylic, termed a buffer layer, to protect the glass from scratching or other damage. As an example of the dimensions, in a typical configuration the diameter of the glass optical fiber is about 125 micrometers, and the diameter of the optical fiber plus the polymer buffer is about 250 micrometers (approximately 0.010 inches).
For such very fine optical fibers, the handling of the optical fiber to avoid damage that might reduce its mechanical strength and/or light transmission properties becomes an important consideration. In one approach, the optical fibers are wound onto a cylindrical or tapered cylindrical bobbin (collectively termed herein a "tapered" cylindrical bobbin even though the angle of the taper may be zero) with many turns adjacent to each other in a side-by-side fashion. After one layer is complete, another layer of optical fiber is wound on top of the first layer, and so on. A weak adhesive is typically applied to the layers of optical fiber, to hold them in place. The final assembly of the bobbin and the wound layers of optical fiber is termed a canister, and the mass of wound optical fiber is termed the fiber pack. When the optical fiber is later to be used, the fiber is payed out from the canister in a direction generally parallel to the axis of the cylinder.
As the optical fiber is payed out from the canister, it naturally follows a helical pattern because the optical fiber continuously unwinds from the bobbin. In some instances, the helical component to the payout of the optical fiber can be undesirable. For example, if the optical fiber is to be dispensed through an opening in the canister wall of small diameter located a few centimeters from the bobbin, the helical motion can cause the optical fiber to rub against the entry of the tube, with possible damage to the optical fiber. Dispensing through a tube or duct is usually not possible if there is too large a helical component to the motion of the optical fiber as it enters the tube. In another example, the helical pattern can produce an increased radar signature, which is undesirable if the optical fiber is being dispensed from a missile in flight.
There is therefore a need for a technique to damp out the helical motion of the optical fiber as it is dispensed from the bobbin in a direction generally parallel to the axis of the bobbin. The approach must be compatible with other aspects of the storage and use of the optical fiber, such as long storage life in a variety of conditions. The present invention fulfills this need, and further provides related advantages.